The incident was reported to the Defence Nuclear Safety Regulator and the Scottish Environmental Protection Agency and the assessed release to the Gare Loch was less on 0.0001% of the base’s approved annual discharge levels.

Earlier, the MoD listed two Category A incidents at Faslane, from 2006 and 2007.

However, the minister said that in “neither event was any radiological contamination evident”.

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He continued: “None of the events caused harm to the health of any member of staff on the Naval Base, or to any member of the public.”

Defence Minister Stuart Andrew (Chris McAndrew/UK Parliament/PA)

In response to parliamentary questions from Ms Brock, the MoD also disclosed there have been 22 fires on its nuclear armed or nuclear powered submarines since June 2015.

“It’s a shocking record of accidents and incidents in places where the most dangerous weapons on the planet are,” Ms Brock said.

“We already knew that there were 505 nuclear safety events on board submarines while they were berthed at Faslane and now we find that there have been another 284 in other locations at Faslane and at Coulport where weapons are handled.”

She added: “One bad accident would be enough to wipe Scotland out and the safety record is appalling.

“Even the risks from the nuclear reactors on board submarines is too high – as the spillage from the effluent barge shows.”